Due to its VOC-reduced character water-based two-component coating compositions based on a binder component and a polyisocyanate cross-linking agent are widespread in industrial and vehicle coating, in particular also in vehicle repair coating. Those coating compositions usually contain binder components with functional groups containing active hydrogen, for example hydroxyl groups. The coating compositions have similar good technological properties as their solvent-borne counter parts, even if some deficiencies still need to be overcome.
Typically the hydroxyl-functional components are based on anionically stabilized polymer dispersions neutralized with volatile or partly volatile amines. In particular for use in vehicle repair coating, a short drying time of the coating at moderate temperatures, for example from room temperature up to approx. 60° C., is desired.
EP 1391469 discloses aqueous binder dispersions containing carboxy-functional copolymers neutralized with triethanolamine as a non-volatile reactive neutralizing amine. In such compositions the triethanolamine can crosslink with the other components of the binder, but the final network contains N-carbon bonds that are prone to yellowing and may hurt durability.
In addition it is known to use reactive diluents with sterically hindered amino groups to reduce curing time. For example, WO 2005/035482 discloses aspartates prepared from primary amines and maleates and their use as reactive components in two-component polyurethane coating compositions, and EP 1616889 discloses hydrophilic polyaspartic esters for use in aqueous two-component coating compositions. However, use of aspartates in two-component coating compositions generally leads to a remarkable reduction in pot life, i.e. a reduction in the time within which the coating composition can still satisfactorily be processed or applied.
Furthermore, it is known to use epoxide-amine-adducts with sterically hindered amino groups as binders with polyisocyanate cross-linkers in two-component coating compositions. For example, EP 0741158 discloses mixtures of hydroxy-functional copolymers and epoxide-amine-adducts having a mass fraction of at least 20% of aliphatic epoxide and/or amine units which comprise at least one tertiary or quaternary carbon atom, as binders for coating compositions and reactive components in adhesives. WO 01/42328 also discloses hindered amine adducts with tertiary alkyl groups as binders for polyurea coating systems. There is no teaching in above two applications to use the binders as neutralizing agents in water borne 2K compositions that are anionically stabilized.
There is accordingly still a requirement for water-based two-component coating compositions, based on a binder component with functional groups containing active hydrogen and polyisocyanate cross-linking agents, which combine an adequate pot-life with a short drying time even at moderate temperatures of for example room temperature or 40° C. to 60° C. Also, the formulation of coating compositions with lower VOC at acceptable spraying viscosities should be possible. The water-based coating compositions should here yield coatings with very good technological properties, such as for example very good hardness and resistance to chemicals and water, and excellent optical appearance. The paint films should be high gloss and brilliant.